‘Busy’ PA-28s can suffer from cracks in the walkway doubler that is underneath the starboard wing skin where the walkway is – all that doubler does is beef up the walkway where everyone, er, walks…

The walkway doubler has, for want of a better word, flutes in it to provide added strength for the foot traffic (nothing to do with flight loads). The flutes are effectively the same (but bigger) as those found in the ailerons, flaps, horizontal stab and rudder skins. If the double cracks, it is normally at the rounded ends of the flutes.

The port wing is the same as the starboard without the walkway doubler skin.

No, I wasn’t refering to the walkway doublers. Two aircraft i know closer developed cracks in the root (》30000 landings on grass though). I think that qualifies as "often on high time training aircraft ;-)

As a PA-28 owner this is of interest. I don’t know if it’s referred to in the other threads, but I’ve always felt that the AAIB’s commentary on the Thruxton crash Thruxton (Passenger behaviour, maybe camera strap caught on controls causing excessive control reversals) was a little ‘last resort’. It’s quite hard to apply excessive control forces in a PA-28 at normal speeds.